1. Technical Field
The invention relates to multiple channel communication systems.
2. Discussion of the Related Art
This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Many digital subscriber line (DSL) communication systems are susceptible to downlink and uplink crosstalk between the local-end telephone lines that connect DSL modems of a central office (CO) to DSL modems at customer premises. The crosstalk may be caused, in part, by inductive coupling between twisted pairs of the local-end telephone lines. The crosstalk can negatively affect DSL communications between the CO and the customer premises in the uplink and the downlink directions. For example, the crosstalk may reduce distances over which DSL communications can be maintained and/or reduce maximum obtainable DSL data transmission rates.
Some DSL communication systems compensate for the undesired effects of such crosstalk in DSL downlink and uplink communications. To perform such compensation, the DSL communication systems typically measure downlink and uplink channel matrices, i.e., HD and HU, respectively. From the downlink channel matrix, HD, the CO may precode downlink DSL communications so that DSL modems of the customer premises will receive DSL data signals substantially free of crosstalk-related distortions. From the uplink channel matrix, HU, the CO may decode received uplink DSL communications to produce DSL data signals substantially free of crosstalk-related distortions.
The measurement of the downlink and uplink channel matrices HD and HU may be performed during the initialization and tracking of a DSL communication session. Typically, a different pair of channel matrices HD and HU is measured for each DSL tone. The measured downlink and uplink channel matrices HD and HU may be updated as DSL communication sessions and corresponding lines are added to or removed from the set of DSL sessions being managed by a CO. The compensation of sets of temporally parallel DSL sessions for crosstalk is often referred to as DSL vectoring.